SYNTHESIS OF THE TETRACHLOROBIS(5-NITROIMIDAZOLE)RUTHENIUM(III) ANION AND SOLUTION CHEMISTRY IN WATER AND METHANOL

The (4-NO(2)ImH)(+) salt of the [RuCl4(5-NO(2)Im)(2)](-) anion was obtained by reacting 4-nitroimidazole (4-NO(2)Im) with activated RuCl3 in aqueous HCl solution. Crystallographic work on the corresponding [P(C6H5)(4)][RuCl4(5-NO(2)Im)(2)] compound (P2/c, a=7.896, b=7.823, c=27.027 Angstrom, beta=100.33 degrees, Z=2, R=0.054) revealed a trans-octahedral coordination about the metal and nitroimidazole binding as the 5-nitro tautomer. The H-1 NMR signals of the anion are broad and considerably displaced upfield by the paramagnetic Ru(III) centre, but they could be used to follow the solvolysis. One Cl- ligand was displaced by a solvent molecule over a period of days in D2O and in CD3OD, but higher solvolysis products were not observed. N6,N6-Dimethyladenine (DMAD) failed to react with [RuCl4(5-NO(2)Im)(2)](-) in D2O and did not perturb the normal aquation process. In CD3OD, a 1:1 complex [RuCl3(DMAD)(5-NO(2)Im)(2)] appeared slowly in a fresh solution, but much faster when DMAD was added to an aged solution, suggesting that the monosolvent species [RuCl3(CD3OD)(5-NO(2)Im)(2)] is actually undergoing substitution. The reaction of RuCl3 with 2-methyl-4(5)-nitroimidazole gave a mixture of at least four unidentified species which could not be separated, showing that the 2-methyl group plays a crucial role in the reactivity in these systems.